1. Field of the Invention PA1 2. Description of the Related Art
The present invention relates to an improvement in a belt tensioner mainly utilized in a belt driving system for an automobile engine.
This kind of belt tensioner is utilized in order to positively transmit a driving force by preventing slack when the driving force is transmitted to a plurality of devices by a single belt. This kind of belt tensioner is disclosed in publications such as Japanese Examined Patent Publication No. 62-2182.
In the conventional belt tensioner disclosed in the above Publication, a tensioner arm is rotationally connected to a stationary member fixed to an engine block and a pulley is rotatably provided on the arm. A torsion spring is provided between the stationary member and the tensioner arm, and the torsion spring urges the tensioner arm rotationally so that the pulley tensions the belt. Also, the torsion spring has a function to urge a damping member secured to the, tensioner arm toward the stationary member, and thereby a damping force for damping the vibration of the tensioner arm, when the tensioner arm swings, is produced.
In the conventional belt tensioner described above, however, since the torsion spring functions both to urge the tensioner arm rotationally and to urge the damping member in order to produce a damping force, when the; torsional degree of the torsion spring is changed according to the rotary position of the tensioner arm, a spring force produced by the torsion spring for urging the damping member is changed. Therefore, a problem arises in that the damping force is changed according to the rotary position of the tensioner arm.